Process for producing metal powder containing iron and molybdenum

ABSTRACT

A FINELY DIVIDED IRON AND MOLYBDENUM ALLOY POWDER WHEREIN THE IRON AND MOLYBDENUM ARE HOMOGENEOUSLY DISTRIBUTED IS PRODUCED BY PROCESS COMPRISING: FORMING AN AQUEOUS SOLUTION OF IRON AND MOLYBDENUM COMPOUND EACH CONTAINING A FUGITIVE ANION, THE WEIGHT RATIO OF IRON TO MOLYBDENUM IN THE SOLUTION IS FROM ABOUT 1:10 TO ABOUT 4:1, THE SOLUTION THAT IS FORMED IS THEREAFTER ATOMIZED INTO DROPLETS HAVING A SIZE OF LESS THAN ABOUT TWO MICRONS IN A CHAMBER CONTAINING A GAS HAVING A TEMPERATURE OF FROM ABOUT 150*C. TO ABOUT 450*C. TO FORM DISCRETE PARTICLES CONTAINING IRON AND MOLYBDENUM AND THEREAFTER HEATING THE PARTICLES IN A REDUCING ATMOSPHERE TO REDUCE THE IRON AND MOLYBDENUM COMPOUNDS AND TO FORM AT LEAST SOME FE3MO2.

United States Patent 3,652,746 PROCESS FOR PRODUCING METAL POWDER CONTAINING IRON AND MOLYBDEN UM Roger B. Bargainnier, Madison, Wis., and William Scheithauer, Jr., Towantla, Pa., assignors to Sylvania Electric Products Inc., Seneca Falls, N.Y. N0 Drawing. Filed Feb. 13, 1970, Ser. No. 11,355 Int. Cl. B0lj 2/04 US. Cl. 264-14 8 Claims ABSTRACT OF THE DISCLOSURE -A finely divided iron and molybdenum alloy powder wherein the iron and molybdenum are homogeneously distributed is produced by a process comprising: forming an aqueous solution of iron and molybdenum compound each containing a fugitive anion, the weight ratio of iron to molybdenum in the solution is from about 1:10 to about 4:1, the solution that is formed is thereafter atomized into droplets having a size of less than about two microns in a chamber containing a gas having a temperature of from about 150 C. to about 450 C. to form discrete particles containing iron and molybdenum and thereafter heating the particles in a reducing atmosphere to reduce the iron and molybdenum compounds and to form at least some Fe Mo CROSS REFERENCES TO RELATED APPLICATIONS In co-pending US. patent application Ser. No. 11,354, filed concurrently herewith, there is disclosed a process for producing metal alloy powders that are formed into metal alloy sheets, bars and the like by normal powder metallurgy techniques. The present invention provides a metal powder that is useful in producing alloys and can be diffused into other metal powders during sintering to form a homogeneous alloy.

BACKGROUND OF THE INVENTION This invention relates to powder metallurgy. More particularly, it relates to a process for producing a metal powder containing a homogeneous solid solution of iron and molybdenum.

Powder metallurgy is a useful method for producing certain metallic materials. For example, essentially all tungsten and molybdenum metal material are prepared via powder metallurgy. In general the process involves the production of particles either in metal form or oxides of metals, isostatic pressing of the particles, then either sintering or reducing and sintering to form a metallic crystalline structure. The materials thus produced are then worked via swaging, drawing, rolling and the like to obtain the desired shape. The foregoing methods are satisfactory for the production of a single component metallic material.

It is known that various alloys of metals have particular properties that are superior to single materials. It is also known that it is desirable to have a homogeneous distribution of each metal component throughout the material. The foregoing homogeneity can be achieved in a variety of ways. For example, in some instances, it is possible to heat each of the metal components to form a liquid state and thereby achieve a homogeneous distribution. Upon cooling a homogeneous distribution does not necessarily occur.

In the beforementioned co-pending patent application there is disclosed a method for producing homogeneous powders that can thereafter be processed via standard powder metallurgy techniques to produce alloys having homogeneity.

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In the production of certain steel alloys, small amounts of molybdenum, generally below about 1%, have been found to be beneficial for some uses. Incorporation of molybdenum in a homogeneous manner has generally been a problem. Techniques such as atomization of all of the metals to form discrete metal particles and diffusion of molybdenum into ferrous base metal have problems associated with each technique. For example, dry blending of an iron alloy without the molybdenum with molybdenum powder, pressing and then sintering results in the production of a material having islands of molybdenum in a matrix of the base metal that is primarily iron with small amounts of nickel. Simultaneous atomization of all of the metals desired results in a powder that can not be adequately processed to form a metal having a homogeneous distribution of all elements because satisfactory isostatic pressing of the coarse irregular particles thus formed cannot normally be achieved. The subsequent sintering does not produce the properties generally desired. In most instances density and homogeneity are not as good as desired. Finer particles have been found to give higher densities.

It is believed therefore that a process that produces an iron and molybdenum containing metal powder that can subsequently be used with a ferrous alloy base material to produce a molybdenum containing iron alloy having a uniform distribution of molybdenum would be an advancement in the art.

SUMMARY OF THE INVENTION In accordance with one aspect of this invention there is provided a process for producing a particular iron and molybendum metal powder having the iron and molybdenum distributed homogeneously throughout. The process comprises forming an aqueous solution containing iron and molybdenum compounds each having a fugitive anion. The weight ratios of iron to molybdenum in said solution are from about 1:10 to about 10:1. The solution is thereafter atomized to a droplet size less than about 2 microns in a chamber containing a gas that has a temperature of between about C. and about 450 C., and thereafter heating the particles in a reducing atmosphere at temperatures and for a time sufi'icient to reduce said iron and molybdenum compounds and to form at least some Fe Mo DESCRIPTION OF THE PREFERRED- EMBODIMENTS An aqueous solution of iron and molybdenum compounds each having a fugitive anion is formed. As used herein a fugitive anion means an anion that will form a compound that will evolve from the material upon application of heat in a reducing atmosphere at temperatures below about 950 C. For example, ferric chloride is a suitable source since the ferric chloride will decompose and the chloride ion will combine with hydrogen or other reducing agents to form a volatile compound. Similarly molybdenum trioxide will decompose and the oxide anion will combine with the reducing agent such as hydrogen to form a volatile compound that is evolved from the metal powder. In general, any iron or molybdenum compound that will decompose under reducing conditions at temperatures below about 950 C. to yield an anion that will form a volatile compound can be used. Iron, phosphates, oxalates, chlorides, nitrates and the like are typical suitable iron compounds useful in this invention. Typical suitable molybdenum compounds useful in this invention include oxides, oxychlorides, chlorides, nitrates and the like.

Since it is desired to obtain an initial homogeneous distribution of the iron and molybdenum, it is necessary for the iron and molybdenum compounds to be dissolved to form a solution. From an economic standpoint it is generally desirable to have a relatively concentrated solution to minimize the water removal. Solutions having total iron and molybdenum concentrations of from about 3 to about 4 pounds per gallon of solution are preferred. More concentrated solutions can result in handling problems while less concentrated solutions add additional costs in water removal, although special economic reasons can make it advantageous to use such solutions.

Although the most homogeneous distribution of iron and molybdenum results from converting the iron and molybdenum compounds to Fe Mo thus having a weight ratio of FezMo of about 122.5, it has been found that satisfactory products can be produced from solution having weight ratios of FezMo of from 1:10 to about 4:1. Choice of the particular ratio will be dependent upon several factors such as the level of molybdenum desired in the final material and the source of raw materials.

After the solution is formed it is atomized to droplets having an average size less than 2 microns into chamber containing a hot gas thereby forming discrete particles having an average particle size less than 2 microns. Although the temperature of the gas in the chamber can vary, it is generally preferred to have an inlet gas temperature of from about 350 C. to about 450 C. and the outlet gas temperature greater than about 150 C. to insure that the particles that are formed have enough of the water removed so that agglomeration of the particles is minimized. The resulting material will be at least partially dehydrated and can in some instances be essentially completely dehydrated. In most instances, essentially all the water in the particles is driven off at temperatures of about 155 C. if the particles are maintained at about 155 C. for a time of about two hours the resulting product is essentially anhydrous. The temperature of the resulting particles will be dependent upon several factors such as the chamber design, flow of gases, flow of solution and size of the particles. In most instances to insure all of the water is driven off, the particles are heated at about 220 C. for a period of about 1 to 2 hours to insure complete dehydration.

The decomposition and reduction step is carried out in a furnace under a reducing atmosphere. Hydrogen is generally supplied to the furnace to yield a slight positive pressure such as about 1-3 inches of water and the particles are heated to a temperature of between about 800 C. to about 950 C. for a period of from about 1 to about hours. Longer periods of reducing can be used but do not appreciably effect the overall quality of the material produced. Shorter reduction times are not generally used since in some instances incomplete reduction can occur.

To more fully illustrate the invention the following detailed example is presented. All parts, percentages and proportions are by weight unless otherwise indicated.

Example 1 About 260 parts of an aqueous ferric chloride solution having a concentration of about 50 parts of iron is heated to about 80 C. About 84 parts of molybdenum trioxide monohydrate is added to the aqueous ferric chloride solution. The iron to molybdenum weight ratio in the solution is measured to be about 1:1. The solution is pumped to a. spray tower and atomized into droplets having a diameter of about 2 microns. The entering air temperature is about 400 C. and the air flow and solution flow are regulated to give an exit air temperature of about 150 C. and results in the formation of discrete particles having an average particle size of less than about 2 microns as measured by the Fisher Sub-Seiver Sizer. The particles are screened to break up any agglomerates that are formed and are transferred to a furnace. Hydrogen is supplied to yield a slight positive pressure of less than about 3 inches of water and the particles are heated to about 220 C. and held for about 2 hours. After the particles are heated to 220 C. for about 2 hours the following heating schedule is followed:

Raise to about 500 C. and maintain for about 2 hours. Raise to about 580 C. and maintain for about 2 hours. Raise to about 900 C. and maintain forabout 2 hours.

i The particles after heating are cooled to room temperature and samples are taken for analysis.

X-ray diffraction analysis of the samples indicates the presence of Fe Mo with small amounts of free iron and free molybednum. Micro-merographs taken at 20,400 magnification indicate homogeneous distribution of iron and molybdenum throughout the particles.

The powder when mixed with appropriate amounts of an iron, nickel and carbide powder material and isostatically pressed with about 40,000 psi. and sintered at about 1100 C. for about 5 hours yields a Fe-Z Ni-0.5 Mo-0.5C alloy having a uniform distribution of materials.

Substantially similar results are achieved when other iron compounds selected from the group consisting of ferric nitrate, ferric oxalate and ferric phosphate are substituted for the ferric chloride in substantially equal stoichiometric amounts. Similarly molybdenum oxychlorides, chlorides and nitrates can be substituted for the molybdenum trioxide.

While there have been shown and described what are at the present considered the preferred embodiments of the invention, it will be obvious to those skilled in the art that various changes and modifications may be made therein without departing from the scope of the invention as defined by the appended claims.

What is claimed is:

1. A process for producing a particulate metal powder containing iron and molybdenum relative homogeneously distributed throughout said powder, said proceswrnprising:

(a) forming an aqueous solution of iron and molybdenum compounds each containing a fugitive anion, the weight ratio of iron to molybdenum in said solution being from about 1:10 to about 4:1;

(b) atomizing said solution to a droplet size less than about two microns in a chamber,

(c) flowing a gas through said chamber, said gas having a temperature of from about C. to about 450 C. to at least partially dehydrate said droplets and form therefrom solid particles containing iron and molybdenum, and

(d) heating said particles in a reducing atmosphere at temperatures and for a time sufiicient to reduce said iron and molybdenum compounds and to form at least some Fe Mo 2. A process according to claim 1 wherein said particles are heated in said reducing atmosphere to a temperature of from about 800 C. to about 950 C. for a period of time of from about 1 to about 10 hours.

3. A process according to claim 2 wherein said iron compound is selected from the group consisting of phosphates, oxalates, chlorides and nitrates.

4. A process according to claim 3 wherein said iron compound is ferric chloride.

5. A process according to claim 2 wherein said molybdenum compound is selected from the group consisting of oxides, oxychlorides, chlorides and nitrates.

6. A process according to claim 5 herein said molybdenum compound is molybdenum trioxide.

7.A process according to claim 6 wherein said iron compound is ferric chloride.

8. A process according to claim 7 wherein said particles are heated in said reducing atmoshpere according 5 to the following schedule, about 220 C. for about 2 3,556,780 1/1971 Holtz 264-13 hours, then at about 500 C. for about 2 hours, then for 3,130,225 4/1964 Friend 264-14 about 580 C. for about 2 hours and at about 900 C.

for about 2 hours. ROBERT F. WHITE, Primary Examiner References Ci d 5 J. R. HALL, Assistant Examiner UNITED STATES PATENTS C1. 3,510,291 5/19 70 Brush 26413 264-13 

